you say you've managed to get FTP access and that you're using the Arras theme.

The Arras theme just got updated so that it'll work with WordPress 3.2. Download it, unzip it, then upload the whole 'arras' folder by FTP to your wp-content/themes directory.
Depending on where your FTP login puts you, it might be under a folder named public_html or htdocs.
The download link to the new version of Arras is at http://www.arrastheme.com/forums/topic7004-arras-theme-151-now-available.html

Try that first and let us know how it goes.

anyway, there's a customer login link on the top right of your host's homepage. that should bring you to the control panel.

Yes, if you add X to the folder name of each plugin it will deactivate them.

Alternatively, download them to your local hard drive and delete them from your web server. Install them back again using the built in WP plugin installer to ensure you have the most recent version and check to see that the recent version is compatible with 3.2 before moving forward to the next plugin.

If the plugin doesn't work or generates errors, contact the plugin author immediately. I just updated 10 of my plugins to ensure they work well with WordPress, it's up to each plugin author to ensure they update their software to work with the new versions of WordPress.

You can disable all plugins in one go by renaming wp-content/plugins to wp-content/pluginsX (or some other name) via FTP (using Filezilla, or your hosts File Manager feature).

If you've not sorted the theme issue, then you could do a similar thing to that - rename all but the twentyeleven folder within the wp-content/themes folder so that WordPress falls back to using the TwentyEleven theme.

At this point, you would hopefully find the site is no longer whitescreening, and that WP dashboard is back up for you to log into.

It's a fact of life, that when the user-friendly administration (WordPress) stuffs up, you might have to get down and dirty with the files, folder and code to fix it for your install. Or hire a web developer who understands the problem, and more importantly, fixes problems like this every day.